The field of the disclosure relates generally to turbomachines, and more particularly, to turbomachines that include a variable geometry vane in a first stage of a power turbine and to methods of assembling turbomachines including a variable geometry vane.
At least some known turbomachines are turbine engines that include a combustor, a compressor coupled upstream from the combustor, a turbine, and a rotor assembly rotatably coupled between the compressor and the turbine. Some known rotor assemblies include a rotor shaft, and a plurality of turbine blade assemblies coupled to the rotor shaft such that a gas flow path is defined between a turbine inlet and a turbine outlet. Each turbine blade assembly includes a plurality of circumferentially-spaced turbine blades that extend outwardly from a rotor disk.
At least some known turbine engines include a plurality of stationary vane assemblies that are oriented between adjacent turbine blade assemblies. Each vane assembly includes a plurality of circumferentially-spaced vanes that extend outwardly from a turbine casing towards a rotor assembly. Each vane is oriented to channel the combustion gases towards adjacent turbine blades to rotate turbine blades. As the combustion gases impact the vanes, at least a portion of the combustion gas flow energy is imparted on the vanes. This flow energy loss reduces the combustion gas flow energy available to rotate the rotor assembly and produce useful work and, thus, reduces an operating efficiency of the turbine.
Some known stationary vane assemblies are variable geometry vane assemblies that facilitate adjusting the cross-sectional area of combustion gases flowing towards the rotor assembly. Each variable geometry vane assembly includes a plurality of circumferentially-spaced variable geometry vanes that are adjustable. One type of variable geometry vane pivots about a pivot axis extending through the variable geometry vane. To facilitate pivoting, the variable geometry vanes are pivotably coupled to the turbine casing and rotor assembly with a clearance space at each end of the variable geometry vanes. As the combustion gases impact the variable geometry vanes, at least a portion of the combustion gases flow over the ends of the variable geometry vanes and through this clearance space. The flow over the ends increases the amount of the combustion gas flow energy that is imparted on the vanes. Additionally, the flow through the clearance space generates tip vortexes and mixing loss. The tip vortexes and mixing loss reduce the operating efficiency of the turbine.